Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 309)

Section 8. Operation
309
Figure 98: Circuit to limit control port input to 5 Vdc
8.1.9 Field Calibration
Read More! Field Calibration of Linear Sensors (FieldCal)
(p. 151)
has complete
information.
Calibration increases accuracy of a measurement device by adjusting its output, or
the measurement of its output, to match independently verified quantities.
Adjusting a sensor output directly is preferred, but not always possible or
practical. By adding FieldCal() or FieldCalStrain() instructions to the CR800
program, a user can easily adjust the measured output of a linear sensors by
modifying multipliers and offsets.
8.1.10 Cabling Effects
Sensor cabling can have significant effects on sensor response and accuracy. This
is usually only a concern with sensors acquired from manufacturers other than
Campbell Scientific. Campbell Scientific sensors are engineered for optimal
performance with factory-installed cables.
8.1.10.1 Analog Sensor Cables
Cable length in analog sensors is most likely to affect the signal settling time. For
more information, see Signal Settling Time
(p. 282).
8.1.10.2 Pulse Sensors
Because of the long interval between switch closures in tipping bucket rain gages,
appreciable capacitance can build up between wires in long cables. A built-up
charge can cause arcing when the switch closes, shortening switch life. As shown
in figure Current Limiting Resistor in a Rain Gage Circuit
(p. 309),
a 100-ohm
resistor is connected in series at the switch to prevent arcing. This resistor is
installed on all rain gages currently sold by Campbell Scientific.
Figure 99: Current limiting resistor in a rain gage circuit